This invention relates to the field of tools used in directional drilling. More specifically, the invention includes a flexible portion disposed in a drill string to facilitate drilling inclined wellbores. The prior art includes several methods for steering a tool string. An embodiment of a bent sub system is generally depicted in FIG. 1a. In this embodiment, a drill string 2000 comprises a bent sub 2050 above the drill bit 2051. A hydraulic motor housed within a bore of a drill string component rotates the drill bit 2051 below the bent sub 2050. As drilling mud is passed through the drill string 2000, the motor turns in response to the flow and rotates a portion 2052 of the drill string 2000 below the bent sub 2050. A portion 2053 of the drilling string 2000 above the bent sub 2050 does not rotate from the motor, but slides through the wellbore as the drill bit 2051 advances into the earth. The bent sub 2050 directs the trajectory of the drill string 2000 in relation to an angle of the bent sub 2050.
An embodiment of a push-the-bit system is generally depicted in FIG. 1b. In this embodiment of a drill string 2100, an extendable pad 2150 is located above the drill bit 2151. Typically, there is more than one extendable pad oriented around an outer surface of the drill string 2100 near the drill bit 2151 that are timed together so as to extend at the same azimuth with relation to the well bore while the drill string 2100 is rotating. Each time an extendable pad 2150 extends, it pushes the drill bit 2151 off course and may be used to control the trajectory of the drill string 2100.
Yet another embodiment for steering a bit includes point-the-bit systems where a drill bit is actively positioned from further up a drill string.
Variations of these systems are disclosed in the following prior art documents. U.S. Pat. No. 5,529,133 to Eddison, which is hereby incorporated by reference for all that it contains, discloses a steerable rotary drilling tool that includes a drill bit mounted on the lower end of a housing by a drive shaft having an articulative coupling that allows the bit's rotation axis to be inclined relative to the rotation axis of the housing, an eccentric weight in the housing that maintains the bit axis pointed in only one direction in space as the bit is turned by the housing, and a clutch system that allows such direction to be changed downhole. A measuring-while-drilling tool is included to allow the progress of the drilling to be monitored at the surface and to allow changing the bit axis or toolface by a selected amount.
U.S. Pat. No. 5,078,650 to Foote which is herein incorporated by reference for all that it contains discloses a universal joint arrangement that includes a first adapter having two projecting support formations; a drive plate having a first pair of matching depressions or pockets is seated with these depressions on the projecting support formations of the first adapter and the drive plate has a second pair of pockets for the projecting support formations of a respective second adapter.
U.S. Pat. No. 7,188,685 to Downton which is herein incorporated by reference for all that it contains discloses a bottom hole assembly that is rotatably adapted for drilling directional boreholes into an earthen formation. It has an upper stabilizer mounted to a collar, and a rotary steerable system. The rotary steerable system has an upper section connected to the collar, a steering section, and a drill bit arranged for drilling the borehole attached to the steering section. The steering section is joined at a swivel with the upper section. The steering section is actively tilted about the swivel. A lower stabilizer is mounted upon the steering section such that the swivel is intermediate the drill bit and the lower stabilizer.